Method of producing molybdenum and molybdenum compounds



Patented Sept. 16, 192 4.

' UNlTED STATES PATENT OFFICE.

'onoaen D. van ARSDALE, ausn 'r. SILL, AND HARLEY A. SILL, or LosANGELES,

' CALIFORNIA.

METHOD OF PRODUCING MOLYBDEN'U' M AND MOLYBDENUM COMPOUNDS.

' No Drawing.

To all whom it may concern.

Be it known that we, GEORGE D. VAN Ans- DALE, RUSH T. SILL, and HARLEYA. SILL, citizens of the United States, residin in Los Angeles, countyof Los Angeles, tate of California, have jointly invented certain newand useful Improvements in Methods of Producing Molybdenum andMolybdenum Compounds, of whichthe following is a specification.

This invention hasfor its general object the provision of an im rovedmethod of extracting molybdenum rom its ores, concentrates or compoundsof the metal; or, in a more specific aspect, to produce molybdenum ormolybdenum compounds which may in themselves be the end of the processor from which the metal may be easily reduced in any of the several.wellknown manners.

The general object'ofthe invention is to produce or make it possible toproduce the metal more inexpensively than is possible with presentmethods of which we are aware. There are also other minor objects of theinvention; but they will be best understood from the followingspecification wherein we describe preferred methods of procedure inaccordance with and illustrative of our invention. e 0 The particularmethod, illustrative of our invention, described in the followingspecification is particularly suitable for obtaining the metal from oresor compounds in which it is present as sulphides, oxides, or as'molybdates such for instance as lead molybdate. The molybdates need notbe roasted-they may be treated in that form. And where we have othercompounds such as sulphides to work with we may either 4 roast to oxidesor they may be fused with sodium carbonate (soda ash for instance) toproduce a sodium molybdate. And the other molybdates, as lead molybdate,wul;- fenite, maybe likewise treated with sodium carbonate to get asodium molybdate. In known ores the metal usually exists .in the form ofsulphide, and in some ores this is accompanied by appreciable amounts ofoxides. The sulphide, molybdenite, can be extracted readily as aconcentrate by known methods; but the oxides cannot be extracted in thisway and ores containing the oxides do not give -a satisfactory recoverywhen treated by concentration- By our method Application filed November6, 1922. Serial No. 599,430.

2. Leaching the resulting compounds (at the start of the process) in asolution to produce a sodium molybdate electrolyte and after the processis in operation leaching with depleted electrolyte; or

2. (corresponding to 1 above) leaching from the fusion product withwater or with acidulated water.

3. Electrolyzing the solution of molybdenum thus made to produce amolybdenum deposit at the cathode, and to regenerate solution for re-useas solvent on fresh ore.

4. Further treatment of the cathode prod not if. desired. Furtherdetails and ramifications of the process are explained hereinafter.

In order to produce a satisfactorily complete roast we find it necessaryto reduce the size of the molybdenum concentrates. Molybdenumconcentrates as usually produced consist of lumps of such large sizethat they cannot be roasted satisfactorily,

since the oxidation results in the .lumps becoming coated with a more orless Impervlous oxide coatlng which prevents access of air to theinterior unroasted sulphide.

l/Vc have therefore found it necessary before roasting to redure thesizes to such a. degree that this result does not take place and so thatthe pieces will roast clear through. The roast is carried out from 760F. to 1040 F., these being approximately the temperatures within whichoxidizing reaction of the sulphide takes place. When roastingunconcentrated ores extraneous heat may be required tomaintain theroasting temperature; but in roasting commercial-concentrates the heatof oxidation may be sufficient to keep up the roasting temperill) llu)

ature, or may even tend to carry the temperatures-too high. During theeriod of oxidation the temperature sho d be ke t as low as possible toavoid volatilization osses and must be kept below the sinteringtemperature of the oxides produced.

The resultant roasted product, under the conditions named, will havemost of its molybdenum in the form of the trioxide M00, soluble in theleaching solution or depleted electrolyte whether alkaline, neutral oracid; and this is also true of the oxidized compounds usually originallypresent in ores.

Then in the second main step of our process, in starting operations, weleach out the roast preferab y with an alkali solution for instance, asolution of caustic soda). his solution is made of sufiicient strengthto react with the M00 to form sodium molybdate and further preferably tohave a sufficient excess of M00 to form a final electrolyte that isdistinctly acid by forming mol bdic acid with the water of the solution.e may in this process use a solution carrying any convenient percentageof molybdenum; we find that about 2-}% M00 is about as low as we care togo for commercially profitable operation and therefore we find itconvenient to start with a solution of about 5% M00 Consequently, as amatter of illustration, we will say here that we use a caustic solutionstrongenough to react with a quantity of calcine equivalent to the 5% ofMoO to produce sodium molybdate and leave enough of the M00 to have afinal distinctly acid solution due to theexcess of M00 forming molybdicacid with the water of the solution. Or free acid, as sulphuric, may beadded to get the desired acid condition. It may be desirable in somecases either to have a neutral solution or even to have a somewhatalkaline solution for the next succeeding step of electrolysis; as wefind we are. able by having a neutral or alkaline solution to produceother compounds that may be desirable. The acidity, alkalinity, orneutrality of the electrolyte may be controlled by properlyproportioning the amounts caustic and M00 as will readily be understood.By control of this solution we may more or less control the nature ofthe electrolytic deposit, to produce mol bdenum, or oxides, or othercompounds. llowever, in general we preferably use a distinctly acidsolution. We find that a small percentage of free acid alsopreventsco-p1ecipitation of some impurities, as sodium.-.. We find about2.5% totalacidity to give good results in the electrolysis.

We may also treat the sulphide directly to form a water solublealkali-molybdate.

Thus we may fuse the sulphide with soda ash to produce a mass containingsodium molybdate and then leach out the mass with water or acidulatedwater to get a solution of sodium molybdate. Likewise we may treat othermolybdates in the samemanner. When we treat for example wulfenite oresor concentrates the product resulting from the fusion with soda ash isleached with water, (or may be leached with regenerated depletedelectrol te 'as hereinafter explained) leaving in t e residue lead,copper, gold, silver and other substances, which residue ma The watersolution of sodium molybdate obtained b treating the fusion mass may beadjuste as to acidity. as explained above by the addition of freesulphuric acid. It will be understood that the leaching operation andthe separation of the solution from the angue may be accomplished in anysuitable apparatus. After the initial starting of the process, inv whicha freshly prepared solution is used, the leaching solution is'providedby operation of the process itself, as will later be understood, and sothis leaching solution as used in the average run of the process willcontain a certain percentage of mol 'bdenum as we do not, in the nextstep of e ectrolysis, aim commercially to take out all of the metal.

Then in the next step of the process by electrolytic action weprecipitate the dissolved metal at the cathode as sesquioxide or otherform of molybdenum or molybdenum compound. The electrolysis may becarried out in any suitable electrolytic apparatus as in an ordinaryelectroy tic cell, using an insoluble anode. Lead or graphite may beused as anode materiaL. The cathode may be made of any one of severalsubstances; for example, sheet iron or aluminum do very well. It ispossible in this step to remove all of the metal, but not economical todo so by continued electrolysis; so we prefer to stop the electrolyticaction when the solution reaches about 2 M00 0perating between 5% and ElMoO gives a good average yield per unit of power. The current densitiesmay be varied but we have found about 1.8 amperes per square foot ofcathode surface to be a satisfactory density for practical use: We havealso found that by heating the electrolyte to about 160 F. it ispossible to obtain an average precipitate be treated separately forother val-- yield of about 1 to 2 lbs. per kilowatt I hour as against ayield of about lb. if the solution is not heated. Under these operatingconditions the cathode deposit consists of molybdenum oxides and maycontain other compounds of the metal, and the metal itself, but isusually mainly hydrated molybdenum sesquioxide. There may be smallamounts of other forms of molybdenum and small amounts of othersubstances also precipitated, depending upon what is present in theelectrolyte. This deposit adheres to the cathode; but by removing anddrying Y use for leaching.

Going back now to the first part of our process we will explain certainvariational and additional steps that may be used. For instance, oresthat carry the metal as lead molybdate do not need to be roasted but maybe treated as described above to produce sodium molybdate; the resultbeing the solution of the molybdenum as sodium molybdate, and leavingthe lead and other valuable constituents in the residues. In thisconnection We may point out one valuable feature of our process; thatthe presence of some other metals, objectionable in known molybdenumprocesses, is not obj ectionable in our process. For instance, ores,carrying copper are objectionable in ordinary methods, but are notobjectionable in our method. Allor most such metals are left in thegangue or are otherwise taken care of at the time of leaching.

In order to remove iron and some other metals that may be objectionablein some cases, We may first leach the calcine with water or acidulatedwater (say 1%% acid). After this leaching, the residue, being theremainder of the calcine that does not go into the water or acidulatedwater leaching'solution, then is leached with depleted electrolyte aspreviously described. If the solution obtained by preliminary leachingcontains appreciable amounts of molybdenum, it may be treated in knownways (forinstance, treatment with an alkali such as caustic soda, orsodium carbonate) to remove iron and then be added to the main solutionfor electrolysis.

Before electrolyzing the sodium molybdate solution we may heat andfilter it to remove any suspended impurities.

- In the step of electrolysis the molybdenum is deposited at the cathodein the form ofmolybdenum or oxides and the solvent is also regenerated.This regenerated solution then goes back into the process, being used toleach more of the calcine, or the. residue of the calcine as aboveexplained; or is joined with the water or acid solution resulting fromthe preliminary sodium carbonate treatment of the ores or concentrates,as above explained; or is used to leach'out the fusion. mass instead ofthe water or ncidulated water as explained above. In this last mentionedcase we may neutralize the metal.

the regenerated depleted electrolyte, if necessary, before leaching, toobviate the possibility of acid present in the leaching solution takingany undesirable impurities out of the mass being leached. Thus the useof the leaching solution is cyclical; and the solution havin is onlynecessary tereafter to add caustic or acid to the process to make up acasual deficiency, or to add some fresh solution to make up for thediscard of a small part of the solution each cycle to prevent buildingup of undesirable impurities. Of course the been once made up it totalor free acidity of the electrolyte diminishes as the M00, is removed inthe electrolyzing step; but the acidity is renewed when new calcine isleached with the depleted electrolyte or when it is joined with theleach solution from the fusion operation, as before described. I

We have stated that we prefer to use an acid electrolyte. We find thatproduction is greater from an acid electrolyte than from a neutral oralkaline one, but find that it is possible to produce a molybdenumdeposit even with an electrolyte distinctly alkaline. However we findthat the nature of the deposit varies with, and to a certain extent canbe controlled by, the degree of acidit or alkalinity of the electrolyte;and so, alt ough the acid electrolyte is preferred for maximum deposit,we do not wish to limit our process specifically or entirely to an acidelectrol te.

The sesquioxlde (M0 0 or other compounds as detached from the cathodemay be marketed in that form or may be used for the production of themetal or compounds of For the production of metallic molybdenum, thesesquioxide which we produce has very considerable advantages. So

far as we are aware the sesquioxide has never been commercially used forproducwe do not make any specific claim in itself,

but we prefer to use hydrogen as the reducmg agent, and the operationmay be carried onin any suitable apparatus. The result of reduction ofthe cathode products is a finely divided powder, which can be reduced tosolid form in various manners n t necessary here to specify.

Having described a invention, we claim:

1. The process for extracting'molybde- I num from concentrates and ores,that inpreferred form of our pounds into oxides, then treating thecalcine with dilute sulphuric acid to remove impurities, then treatingthe residue from the acid treatment to form an acid solution of sodiummolybdate, then warming the resulting solution and electrolyzing it toprecipitate molybdenum compounds at the cathode and to regenerate thedepleted electrolyte for reuse as a solvent; then drying, dehydrating,and removing the deposit from the cathode.

' 2. The process for extracting molybdenum from concentrates and ores,that includes roastin to convert sulphide compounds into oxides, thentreating the calcine with dilute sulphuric acid to remove impurities,then separating such impurities from the resultingsolution, thentreating the residue from the acid treatment to form an acid solution ofsodium molybdate, then warming the resulting solution and electrolyzingit together with the solution resulting fromthe first leaching toprecipitate molybdenum compounds at the cathode and to regenerate thedepleted electrolyte for reuse as a solvent; then drying, dehydrating,and removing the deposit from the cathode.

3. The process for extracting molybdenum from concentrates and ores,that includes roasting to convert sulphide compounds into oxides, thentreating the calcine with dilute sulphuric acid to remove impurities,then treating the residue from the acid treatment with a depletedelectrolytic solution, then separating the gangue from the solution,then warming the resulting solution and electrolyzing it toprecipitatemolybdenum compounds at the cathode and to regenerate the depletedelectrolyte for reuse as a solvent; then drying, dehydrating, andremoving the deposit from the cathode.-

v 4. The process for extracting molybdenum from concentrates and oresthat includes forming a solution of an alkalimolybdenum compound, thenwarming the solution and electrolyzing it 't0 produce a molybdenumdeposit and to regenerate the dep eted electrolyte for reuse as asolvent, and then using the regenerated solution for the formation ofmore solution of alkalimolybdenum compound for continued practice of theprocess. 5. The process for extractingmolybdenum from concentrates andores that in cludes forming a. solution of an alkali molybdenumcompound, with a definite total acidity, then warming the solution andclectrolyzing it to produce .a molybdenum deposit and to regenerate thedepleted electrolyte for reuse as a solvent, and then using theregenerated solution for the formation of more solution ofalkali-molybdenum compound for continued practice of the process.

6. The process for extracting molybdenum from concentrates and ores,that includes conversion of sul hide compounds into oxides, then (toinitia y start the process) dissolving the oxides in-a sodium h droxidesolution to form a sodium molybdate solution with an excess of theoxides to form free molybdic acid to ive the solution a free acidity;then electro yzing the solution to precipitate molybdenumcompounds atthe cathode and to regenerate the depleted solution for further use as asolvent; and then using the regenerated solvent to dissolve furtheroxides for the continued practice of the process, the acidity of theelectrolyte being maintained at each dissolving operation by the use ofan excess of the oxides.

7. The process for extracting molybdenum from concentrates and ores,that includes conversion to a soluble alkali-molybdate and the formationof a solution of the molybdate, said solution having a free acidity,then electrolyzing the solution to precipitatemolybdenum compounds atthe cathode and to regenerate the depleted electrolyte for reuse as asolvent, then using the regenerated solvent to form more solution of thealkali molybdate for the continued practice of the process, maintainingat each solution operation the free acidity. of the solution.

a 8. The process for extracting molybdenum from concentrates and ores,that includes the conversion of sulphides into oxides, then treating thecalcine with dilute sulphuric, acid to remove impurities, separating theimpurities from the resulting solution, treating the residue 'from theacid treatment with an alkali solution to form an alkali-molybdatesolution, the oxides being used in excess to give the solution a free'and co-regenerate the depleted electrolyte for reuse as a solvent, thenusing the regenerated solvent to dissolve more of the oxides,maintaining the free acidity of the solution at each dissolving oration.

9. The process 0 treating molybdenum oxides-soluble in an alkalisolution, that includes dissolving the oxides in an alkali solution toproduce an alkali-molybdate solution, the oxide bein .used in excess toform free molybdic aei to make the solution definitely acid; and thenelectrolyzmg the resultant solution.

10. The process of treating-molybdenum oxides soluble in an alkalisolution, that includes dissolving the. oxides in an alkali solution toproduce an alkali-molybdate solution, the oxides being used in excess toform. free molybdio acid to make the solution definitely acid; thenelectrolyzing the resultant solution to produce a cathode product and toregenerate the depleted electrolyte for reuse as a solvent, and thenusing the regeneratedsolution to dissolve more of the oxides forcontinued ractice of the process, the acidity being maintained by use ofan excess of the oxides.

11. The process for extracting molybdenum from concentrates and ores,that includes treatment with sodium carbonate to form sodium molybdate,forming a solution of the molybdate, electrolyzing the solution toproduce a cathode; product and to regenerate the depleted electrolytefor further use in the process, and then using the regenerated solutionto dissolve more sodium molybdate in the continued practice of the proc.

12. The p for extracting molybdenum from concentrates and ores, thatincludes fusion of a molybdate carrying ore or concentrate with sodiumcarbonate to form a a containing sodium molybdate,

leaching the mass to form a solution of sodium molybdate, thenelectrolyzing the solution to produce a cathode product and toregenerate the depleted solution for further use.

13. The process for extracting molybdenum from concentrates and oresthat includes forming a solution of an alkali molybdenum compound, thenelectrolyzing thesolution to product a molybdenum deposit andto'regenerate the depleted electrolyte for reuse as a solvent, and thenusing the regenerated solution for the formation of more solution ofalkali-molybdenum compound for continued practice of the process.

In witness that we claim the foregoing we have hereunto subscribed ournames this 27th day of October, 1922.

GEORGE D. VAN ABSDALE. RUSH T, SILL. HARLEY A. SILL. Witnesses: W. E.Hams, ARTHUR K. Lossnnm, S. J. Mar.

